S. Kaseb

Solar heat gain through vertical cylindrical glass

Abstract Spaces with nonplanar glazed envelopes are frequently encountered in contemporary buildings. Such spaces represent a problem when calculating the solar heat gain in the course of estimating the cooling or heating load; and hence, sizing of cooling or heating systems. The calculation, using the information currently available in the literature, is tedious and⧹or approximate. In the present work, the computational procedure for evaluating the solar heat gain to a space having a vertical cylindrical glass envelope is established, and, a computer program is coded to carry out the necessary computations and yield the results in a detailed usable form. The program is versatile and allows for the arbitrary variation of all pertinent parameters.

HelioTrough thermal performance compared to EuroTrough

Parabolic troughs are the most mature technology and have lowest cost compared to other technologies. A comparison between EuroTrough and HelioTrough is carried out in this work. An energy balance model for the troughs absorber tube is used to estimate the optical and thermal losses from the collector. Engineering Equation Solver (EES) was used as a tool to simulate the trough. Results show that the thermal losses from the HelioTrough are more that loss from EuroTrough. Although this fact, the total energy gained from the HelioTrough is much more than EuroTrough.

Numerical predictions of turbulent flow and heat transfer in circular pipes using a low Reynolds number two-equation model of turbulence

The present paper is concerned with the numerical simulations of the turbulent flow and heat transfer in circular pipes using a low Reynolds number model for turbulence kinetic energy and its dissipation rate. Unlike the high Reynolds number turbulence models, the present solution procedure requires no special treatments near the pipe walls; i.e., no wall functions are needed to simulate the turbulent flow and heat transfer at the pipe walls. It is well known that the type of the wall function has been criticized on the basis that the obtained solution is essentially dependent on some adjustable tuning model constants. The present low Reynolds number model takes the solution up to the walls without any abrupt changes in the axial velocity and temperature profiles. Finite-volume equations are derived for the conservation equations of the mass continuity, axial and radial velocity components, temperature, turbulence kinetic energy and its dissipation rate. The resulting finite-volume equations are solved iteratively using a tri-diagonal matrix algorithm. The obtained results are considered converged when the errors are less than 0.1 percent. The converged radial profiles of the gas temperature, the axial velocity and the axial profiles of the Nusselt number, mean bulk temperature and wall heat flux are presented for six fixed values of the Reynolds numbers. Moreover, the axial profiles of the Nusselt number are presented for six values of the Reynolds number. The

Numerical Predictions of Hydrogen-Air Rectangular Channel Flows Augmented by Catalytic Surface Reactions

Catalytic combustion of hydrogen-air boundary layers involves the adsorption of hydrogen and oxygen into a platinum coated surface, chemical reactions of the adsorbed species and the desorption of the resulting products. Readsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners and catalytic reactors that use low equivalence ratios. In this case the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitrogen oxides. The present paper is concerned with the numerical computations of momentum transfer, heat transfer and chemical reactions in rectangular channel flows of hydrogen-air mixtures. Chemical reactions are included in the gas phase as well as on the solid platinum surfaces. In the gas phase, eight species are involved in 26 elementary reactions. On the platinum hot surfaces, additional surface species are included that are involved in 16 additional surface chemical reactions. The platinum surface temperature distribution is pre-specified, while the properties of the reacting flow are computed. The flow configuration investigated in the present paper is that of a rectangular channel burner. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Hybrid differencing is used to ensure that the finite-difference coefficients are always positive or equal to zero to reflect the real effect of neighboring nodes on a typical central node. The finite-volume equations of the reacting gas flow properties are solved by a combined iterative-marching algorithm. On the platinum surfaces, surface species balance equations, under steady-state conditions, are solved numerically. A non-uniform computational grid is used, concentrating most of the nodes in the boundary sub-layer adjoining the catalytic surfaces. The channel flow computational results are compared with recent detailed experimental data for similar geometry. In this case, the catalytic surface temperature profile along the x-axis was measured accurately and is used in the present work as the boundary condition for the gas phase energy equation. The present numerical results for the gas temperature, water vapor mole fraction and hydrogen mole fraction are compared with the corresponding experimental data. In general, the agreement is very good especially in the first 105 millimeters. However, some differences are observed in the vicinity of the exit section of the rectangular channel. The numerical results show that the production of water vapor is very fast near the entrance section flowed by a much slower reaction rate. Gas phase ignition is noticed near the catalytic surface at a streamwise distance of about 120 mm. This gas-phase ignition manifests itself as a sudden increase in the mole fractions of OH, H and O.Copyright